3,873 research outputs found
Two-Dimensional Confinement of 3d1 Electrons in LaTiO3/LaAlO3 Multilayers
We report spectroscopic ellipsometry measurements of the anisotropy of the
interband transitions parallel and perpendicular to the planes of
(LaTiO3)n(LaAlO3)5 multilayers with n = 1-3. These provide direct information
about the electronic structure of the two-dimensional (2D) 3d^1 state of the Ti
ions. In combination with LDA+U calculations, we suggest that 2D confinement in
the TiO2 slabs lifts the degeneracy of the t_{2g} states leaving only the
planar d_xy orbitals occupied. We outline that these multilayers can serve as a
model system for the study of the t_{2g} 2D Hubbard model.Comment: 7 pages, 4 figures. Accepted for publication in Phys. Rev. Let
Dirac Electrons on a Sharply Edged Surface of Topological Insulators
An unpaired gapless Dirac electron emergent at the surface of a strong
topological insulator (STI) is protected by the bulk-surface correspondence and
believed to be immune to backward scattering. It is less obvious, however, and
yet to be verified explicitly whether such a gapless Dirac state is smoothly
extended over the entire surface when the surface is composed of more than a
single facet with different orientations in contact with one another at sharp
corner edges (typically forming a steplike structure). In the realistic
situation that we consider, the anisotropy of the sample leads to different
group velocities in each of such facets. Here, we propose that much insight on
this issue can be obtained by studying the electronic states on a hyperbolic
surface of an STI. By explicitly constructing the surface effective
Hamiltonian, we demonstrate that no backward scattering takes place at a
concave step edge. A strong renormalization of the velocity in the
close vicinity of the step edge is also suggested.Comment: 4 pages, 2 figures, to be published in J. Phys. Soc. Jp
Effects of oxygen-reducing atmosphere annealing on LaMnO epitaxial thin films
We investigated the effects of annealing on LaMnO epitaxial thin films
grown by pulsed laser deposition and propose an efficient method of
characterizing their stoichiometry. Structural, magnetic, and optical
properties coherently indicate non-stoichiometric ferromagnetic and
semiconducting phases for as-grown LaMnO films. By annealing in an
oxygen-reducing atmosphere, we recovered the antiferromagnetic and insulating
phases of bulk-like stoichiometric LaMnO. We show that non-destructive
optical spectroscopy at room temperature is one of the most convenient tools
for identifying the phases of LaMnO films. Our results serve as a
prerequisite in studying LaMnO based heterostructures grown by pulsed laser
deposition.Comment: 10 pages including 3 figures, accepted in J. Phys. D: Appl. Phy
Electronic structure and anomalous band-edge absorption feature in multiferroic MnWO4: An optical spectroscopic study
We investigated the electronic structure and lattice dynamics of multiferroic
MnWO4 by optical spectroscopy. With variation of polarization, temperature, and
magnetic field, we obtained optical responses over a wide range of photon
energies. The electronic structure of MnWO4 near to the Fermi level was
examined, with inter-band transitions identified in optical conductivity
spectra above a band-gap of 2.5 eV. As for the lattice dynamics, we identified
all the infrared transverse optical phonon modes available according to the
group-theory analysis. Although we did not observe much change in global
electronic structure across the phase transition temperatures, an optical
absorption at around 2.2 eV showed an evident change depending upon the spin
configuration and magnetic field. The behavior of this band-edge absorption
indicates that spin-orbit coupling plays an important role in multiferroic
MnWO4.Comment: Accepted for publication in Physical Review B. 19 pages including 6
figure
Synergistic effects of longitudinal amyloid and vascular changes on lobar microbleeds
OBJECTIVE: To determine whether amyloid and hypertensive cerebral small vessel disease (hCSVD) changes synergistically affect the progression of lobar microbleeds in patients with subcortical vascular mild cognitive impairment (svMCI).
METHODS: Among 72 patients with svMCI who underwent brain MRI and [11C] Pittsburgh compound B (PiB)–PET, 52 (72.2%) completed the third year of follow-up. These patients were evaluated by annual neuropsychological testing, brain MRI, and follow-up PiB-PET.
RESULTS: Over 3 years, 31 of 52 patients (59.6%) had incident cerebral microbleeds (CMBs) in the lobar and deep regions. Both baseline and longitudinal changes in lacune numbers were associated with increased numbers of lobar and deep microbleeds, while baseline and longitudinal changes in PiB uptake ratio were associated only with the progression of lobar microbleeds, especially in the temporal, parietal, and occipital areas. Regional white matter hyperintensity severity was also associated with regional lobar CMBs in the parietal and occipital regions. There were interactive effects between baseline and longitudinal lacune number and PiB retention on lobar microbleed progression. Increased lobar, but not deep, CMBs were associated with decreased scores in the digit span backward task and Rey-Osterrieth Complex Figure Test.
CONCLUSIONS: Our findings suggest that amyloid-related pathology and hCSVD have synergistic effects on the progression of lobar microbleeds, providing new clinical insight into the interaction between amyloid burden and hCSVD on CMB progression and cognitive decline with implications for developing effective prevention strategies
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